scholarly journals Photochemistry of 2-Oxoacetates: from Mechanistic Insights to Profragrances and Bursting Capsules

2020 ◽  
Vol 74 (1) ◽  
pp. 39-48 ◽  
Author(s):  
Andreas Herrmann
Keyword(s):  
Carbonyl Compounds ◽  
Hydrogen Abstraction ◽  
Core Shell ◽  
Type Ii ◽  
Stimuli Responsive ◽  
Capsule Wall ◽  
Polymer Conjugates ◽  
Gas Formation ◽  
Norrish Type ◽  
Intramolecular Hydrogen

Photoirradiation of 2-oxoacetates (α-ketoesters) with UV-A light proceeds via an intramolecular hydrogen abstraction of the triplet state in a Norrish type II pathway to form carbonyl compounds, carbon monoxide and/or dioxide, and a series of other side products. This review gives a detailed overview of the mechanistic aspects of photooxidation by explaining the pathways that yield the major products formed in the presence or absence of oxygen. Furthermore, it demonstrates how the photoreaction can be used for the light-induced controlled release of fragrances from non-polymeric profragrances, polymer conjugates and core-shell microcapsules in applications of functional perfumery. In the case of microcapsules, the gas formation accompanying the Norrish type II fragmentation can generate an overpressure that expands or cleaves the capsule wall to release fragrances and thus provides access to multi-stimuli responsive delivery systems.

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

Photolysis of 4-Methyl 3-Hexanone and 2-Methoxy 3-Pentanone in Hydrocarbon Solution

1971 ◽  
Vol 49 (8) ◽  
pp. 1310-1314 ◽  
Author(s):  
L. P-Y. Lee ◽  
B. McAneney ◽  
J. E. Guillet
Keyword(s):  
Quantum Yield ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Type Ii ◽  
Cage Effect ◽  
Predominant Type ◽  
Norrish Type ◽  
Hydrocarbon Solution ◽  
Membered Transition State ◽  
Made In

Studies of the photolysis of 4-methyl 3-hexanone and the iso-electronic 2-methoxy 3-pentanone have been made in hydrocarbon solution using light of wavelength 313 nm. The latter compound gives only Norrish type II products with a quantum yield of 0.19 ±.01. The former gives a predominance of type I products with a total quantum yield of 0.23 ±.01 and the quantum yield for type II is reduced to 0.10 ±.01. The predominant type I reaction appears to involve α-scission to give an ethyl and a 2-methyl butyryl radical, which suggests a "cage effect". It is suggested that the reason for the suppression of the type I reaction in 2-methoxy 3-pentanone is the greater ease of γ-hydrogen abstraction due to the presence of the oxygen atom in a six-membered transition state.

Quantitative aspects of alkylperoxy radical isomerization during hydrocarbon combustion

1967 ◽  
Vol 300 (1463) ◽  
pp. 455-467 ◽  
Keyword(s):  
Oxygen Atom ◽  
Carbonyl Compounds ◽  
Hydrogen Abstraction ◽  
Carbon Number ◽  
Oxidation Mechanism ◽  
Intramolecular Rearrangement ◽  
Cool Flame ◽  
Hydrocarbon Combustion ◽  
Intramolecular Hydrogen ◽  
Oxidative Attack

Detailed studies of the distribution of the products formed in the different regimes of combustion of n -pentane indicate the importance in the overall oxidation mechanism of the isomerization of amylperoxy radicals. It has been shown that C 5 O -heterocycles and C 5 alkenes are formed as a result of the intramolecular rearrangement of such radicals but that O -heterocycles, carbonyl compounds and alkenes of carbon-number less than five are produced in other ways. The experimental results suggest that, under cool-flame conditions where the yields of C 5 O -heterocycles and C 5 alkenes are highest, between 40 and 50% of the initially formed amylperoxy radicals undergo isomerization followed either by O—O bond fission and cyclization or by C—O bond fission. Then nature and amounts of the various O -heterocyclic products formed from n -pentane enable deductions to be made firstly as to the extents of initial oxidative attack of the hydrocarbon at different skeletal positions and secondly as to the relative susceptibilities of the different C—H groups to intramolecular hydrogen abstraction by the outer oxygen atom of the amylperoxy radical.

Modification of photochemical reactivity through the use of clathrates: the Norrish type I and type II reactions in Dianin's compound

1985 ◽  
Vol 63 (10) ◽  
pp. 2719-2725 ◽  
Author(s):  
P. C. Goswami ◽  
Paul de Mayo ◽  
N. Ramnath ◽  
G. Bernard ◽  
N. Omkaram ◽  
...  
Keyword(s):  
Inclusion Complexes ◽  
Hydrogen Abstraction ◽  
Photochemical Reactions ◽  
Type I ◽  
Type Ii ◽  
Guest Molecules ◽  
Photochemical Reactivity ◽  
Norrish Type ◽  
Restricted Environment ◽  
Dianin's Compound

Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) serves as host in a series of well-defined clathrate inclusion complexes with eleven linear, as well as branched chain, phenyl alkyl ketone guest molecules, chosen for their ability to undergo the Norrish type I and type II photochemical reactions in solution. The photochemical reactivity of the guest ketones within the clathrate cavity was determined by irradiation of the inclusion complexes in the solid state. The results were compared to the photoreactivity of the ketones in polar as well as nonpolar liquid media. In general, the inclusion complex medium brings about an enhancement of type I over type II reactivity and causes an increase in type II fragmentation compared to type II cyclization. This change in reactivity is interpreted as resulting from the relatively restricted environment of the clathrate cavity coupled with the greater motion required for the type II process (γ-hydrogen abstraction) compared to the type I reaction (α-cleavage), as well as from the greater steric requirements for type II cyclization (cyclobutanol formation) as compared to type II cleavage (1,4-hydroxybiradical scission).

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